Ink set

ABSTRACT

An ink set comprising a black ink and a color ink, wherein the black ink comprises an aqueous dispersion of water-insoluble vinyl polymer particles containing an oil-soluble black dye or carbon black, the vinyl polymer particles have an ionicity opposite to that of the color ink, and the vinyl polymer comprises a water-insoluble vinyl polymer prepared by copolymerizing (a) a salt forming group-containing monomer, (b) a monomer represented by the formula (I):  
     CH 2 ═C(R 1 )COO(R 2 O) p R 3   (I)  
     wherein R 1  is hydrogen atom or a lower alkyl group, R 2  is a divalent hydrocarbon group which may have a hetero-atom, R 3  is a monovalent hydrocarbon group which may have a hetero-atom, and p is a number of 1 to 60, (c) a macromer, and (d) a monomer copolymerizable with these monomers. The ink set can be used as an ink set for inkjet recording, which is excellent in not only fixing abilities and water resistance, but also bleeding resistance and jettability, and can form very clear printouts.

TECHNICAL FIELD

[0001] The present invention relates to an ink set. More specifically,the present invention relates to an ink set which can be suitably usedfor an ink set for inkjet recording.

BACKGROUND ART

[0002] Inkjet recording is a recording system for forming characters orimages, comprising directly jetting ink droplets from very fine nozzlesto a recording medium, and depositing the ink droplets on the recordingmedium. This system has advantages that not only the used device showsexcellent operability at a low level of noise, but also the colorationis facilitated and plain paper can be used as a recording medium.Therefore, this system has been widely used in the recent years.

[0003] As an ink set comprising a black ink and a color ink usable forcolor inkjet printers, there have been known an ink set comprising anacidic black ink comprising an acidic carbon black, a basic surfactantand a water-soluble organic solvent, and a basic color ink (JapanesePatent Laid-Open No. Hei 9-183224); an ink set comprising a black inkcomprising a self-dispersible carbon black in which at least onehydrophilic group is bonded directly or via the other group of atoms tothe surface of the carbon black, and a color ink comprising a coloranthaving a polarity opposite to the colorant used in the black ink(Japanese Patent Laid-Open No. Hei 10-140064); and the like.

[0004] However, the printouts formed by using these inks are wrongespecially in fixing abilities such as rubbing resistance andhigh-lighter fastness in the black ink, and are not sufficientlysatisfactory in these properties, while printouts formed by using thereink sets are excellent in bleeding resistance.

DISCLOSURE OF INVENTION

[0005] An object of the present invention is to provide an ink set forinkjet recording, which is excellent in not only fixing abilities andwater resistance, but also bleeding resistance and jettability, and canform very clear printouts.

[0006] The present invention relates to an ink set comprising a blackink and a color ink, wherein the black ink comprises an aqueousdispersion of water-insoluble vinyl polymer particles containing anoil-soluble black dye or carbon black, the vinyl polymer particles havean ionicity opposite to that of the color ink, and the vinyl polymercomprises a water-insoluble vinyl polymer prepared by copolymerizing (a)a salt forming group-containing monomer [hereinafter referred to ascomponent (a)], (b) a monomer represented by the formula (I):

CH₂═C(R¹)COO(R²O)_(p)R³  (I)

[0007] wherein R¹ is hydrogen atom or a lower alkyl group, R² is adivalent hydrocarbon group which may have a hetero-atom, R³ is amonovalent hydrocarbon group which may have a hetero-atom, and p is anumber of 1 to 60 [hereinafter referred to as component (b)], (c) amacromer [hereinafter referred to as component (c)], and (d) a monomercopolymerizable with these monomers [hereinafter referred to ascomponent (d)].

BEST MODE FOR CARRYING OUT THE INVENTION

[0008] As a vinyl polymer used in the aqueous dispersion, awater-insoluble vinyl polymer is used. In order to obtain a water-basedink having both high fixing ability and high dispersion stability, thereis used a water-insoluble vinyl polymer obtained by copolymerizing thecomponent (a), the component (b), the component (c) and the component(d).

[0009] The salt-forming group refers to a group which can form acationic group or an anionic group when the group is neutralized with anacid or a base.

[0010] Representative examples of the component (a) include the cationicmonomers and the anionic monomers described in page 5, column 7, line 24to column 8, line 29 of Japanese Patent Laid-Open No. Hei 9-286939.

[0011] The cationic monomer includes tertiary amine-containingunsaturated monomers, ammonium salt-containing unsaturated monomers, andthe like. Among them, N,N-dimethylaminoethyl acrylate,N,N-dimethylaminoethyl methacrylate, N-(N′,N′-dimethylaminopropyl)acrylamide, N-(N′,N′-dimethylaminopropyl) methacrylamide andvinylpyrrolidone are preferable.

[0012] The anionic monomer includes unsaturated carboxylic acidmonomers, unsaturated sulfonic acid monomers, unsaturated phosphoricacid monomers, and the like. Among them, unsaturated carboxylic acidmonomers, especially acrylic acid and methacrylic acid are preferable.

[0013] The component (b) exhibits an excellent effect of suppressing thegeneration of distortion even when printing is continuously carried outbecause the component (b) increases the jetting stability of thewater-based ink of the present invention.

[0014] In the formula (I), R¹ is hydrogen atom or a lower alkyl group.The lower alkyl group includes linear or branched alkyl groups having 1to 4 carbon atoms.

[0015] R² is a divalent hydrocarbon group which may have a hetero-atom.The hetero-atom includes, for example, nitrogen atom, oxygen atom, ahalogen atom and sulfur atom.

[0016] Representative examples of R² include an aromatic ring having 6to 30 carbon atoms, which may have a substituent; a heterocyclic ringhaving 3 to 30 carbon atoms, which may have a substituent; and analkylene group having 1 to 30 carbon atoms, which may have asubstituent. These rings or groups may be used in combination of atleast two kinds. The substituent includes an aromatic ring having 6 to29 carbon atoms; a heterocyclic ring having 3 to 29 carbon atoms; analkyl group having 1 to 29 carbon atoms; a halogen atom; amino group,and the like.

[0017] Preferred examples of R² include a phenylene group which may havea substituent having 1 to 24 carbon atoms; an aliphatic alkylene grouphaving 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms; anaromatic ring-containing alkylene group having 7 to 30 carbon atoms; anda heterocyclic ring-containing alkylene group having 4 to 30 carbonatoms.

[0018] Preferred examples of R²O group include alkylene oxide groupshaving 2 to 7 carbon atoms, such as ethylene oxide group, (iso)propyleneoxide group, tetramethylene oxide group, heptamethylene oxide group,hexamethylene oxide group, and combinations of at least two kinds ofthese alkylene oxide groups; phenylene oxide group; and the like.

[0019] R³ is a monovalent hydrocarbon group which may have ahetero-atom. The hetero-atom includes nitrogen atom, oxygen atom andsulfur atom.

[0020] Representative examples of R³ include an aromatic ring having 6to 30 carbon atoms, which may have a substituent; a heterocyclic ringhaving 3 to 30 carbon atoms, which may have a substituent; and an alkylgroup having 1 to 30 carbon atoms, which may have a substituent. Thesubstituent includes an aromatic ring having 6 to 29 carbon atoms; aheterocyclic ring having 4 to 29 carbon atoms; a halogen atom; aminogroup, and the like.

[0021] Preferred examples of R³ include phenyl group, an aliphatic alkylgroup having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, anaromatic ring-containing alkyl group having 7 to 30 carbon atoms, and aheterocyclic ring-containing alkyl group having 4 to 30 carbon atoms.

[0022] More preferred examples of R³ include alkyl groups having 1 to 6carbon atoms, such as methyl group, ethyl group, (iso)propyl group,(iso)butyl group, (iso)pentyl group and (iso)hexyl group; phenyl group,and the like.

[0023] p is a number of 1 to 60, out of which a number of 1 to 30 ispreferable.

[0024] Concrete examples of the monomer represented by the formula (I)include methoxypolyethylene glycol (1-30: p value in the formula (I),hereinafter referred to the same) (meth)acrylates,methoxypolytetramethylene glycol (1-30) (meth)acrylates,ethoxypolyethylene glycol (1-30) (meth)acrylates,(iso)propoxypolyethylene glycol (1-30) (meth)acrylates,butoxypolyethylene glycol (1-30) (meth)acrylates, methoxypolypropyleneglycol (1-30) (meth)acrylates, propoxypolypropylene oxide (1-30)(meth)acrylates, methoxy(ethylene glycol-propylene glycol copolymer)(1-30, out of which ethylene glycol: 1-29) (meth)acrylates, and thelike. These monomers can be used alone or in admixture of at least twokinds. Among them, methoxypolyethylene glycol (1-30) (meth)acrylates arepreferable. Incidentally, the term “(meth)acrylate” as used herein meansacrylate or methacrylate. Also, the term “(iso)propoxy” as used hereinmeans n-propoxy or isopropoxy.

[0025] The component (c) includes macromers which are monomers having apolymerizable unsaturated group and a number-average molecular weight of500 to 100000, preferably 1000 to 10000. Among them, a silicone macromerrepresented by the formula (II):

X(Y)_(q)Si(R⁴)_(3-r)(Z)_(r)  (II)

[0026] wherein X is a polymerizable unsaturated group; Y is a divalentgroup; each of R⁴ is independently hydrogen atom, a lower alkyl group,an aryl group or an alkoxy group, respectively; Z is a monovalentsiloxane polymer residue having a number-average molecular weight of atleast 500; q is 0 or 1; and r is an integer of 1 to 3,

[0027] and/or a styrenic macromer having a polymerizable functionalgroup at one end is preferable.

[0028] The number-average molecular weight of the macromer is determinedby gel chromatography using polystyrene as a standard substance andchloroform containing 1 mmol/L of dodecyldimethylamine as a solvent.

[0029] The silicone macromer can be favorably used from the viewpoint ofpreventing scorching on the printer head of an inkjet printer.

[0030] In the silicone macromer represented by the formula (II), Xincludes a monovalent unsaturated hydrocarbon group having 2 to 6 carbonatoms, such as CH₂═CH— group and CH₂═C(CH₃)— group. Y includes divalentgroups such as —COO— group, a —COOC_(a)H_(2a)— group, wherein a is aninteger of 1 to 5, and a phenylene group. Among them, —COOC₃H₆— ispreferable. R⁴ includes hydrogen atom; a lower alkyl group having 1 to 5carbon atoms, such as methyl group and ethyl group; an aryl group having6 to 20 carbon atoms, such as phenyl group; an alkoxy group having 1 to20 carbon atoms, such as methoxy group, and the like. Among them, methylgroup is preferable. Z is preferably a monovalent dimethylsiloxanepolymer residue having a number-average molecular weight of 500 to 5000.q is 0 or 1, and preferably 1. r is an integer of 1 to 3, and preferably1.

[0031] Representative examples of the silicone macromer include asilicone macromer represented by the formula (II-1):

CH₂═CR⁵—COOC₃H₆—[Si(R⁶)₂-O]_(b)—Si(R⁶)₃  (II-1)

[0032] wherein R⁵ is hydrogen atom or methyl group; each of R⁶ isindependently hydrogen atom or a lower alkyl group having 1 to 5 carbonatoms, respectively; and b is a number of 5 to 65;

[0033] a silicone macromer represented by the formula (II-2):

CH₂═CR⁵—COO—[Si(R⁶)₂—O]_(b)—Si(R⁶)₃  (II-2)

[0034] wherein R⁵, R⁶ and b are the same as defined above;

[0035] a silicone macromer represented by the formula (II-3):

CH₂═CR⁵—Ph—[Si(R⁶)₂—O]_(b)—Si(R⁶)₃  (II-3)

[0036] wherein Ph is a phenylene group; and R⁵, R⁶ and b are the same asdefined above;

[0037] a silicone macromer represented by the formula (II-4):

CH₂═CR⁵—COOC₃H₆—Si(OE)₃  (II-4)

[0038] wherein R⁵ is the same as defined above; E is a group representedby the formula: —[Si(R⁵)₂O]_(c)—Si(R⁵)₃, wherein R⁵ is the same asdefined above, and c is a number of 5 to 65;

[0039] and the like.

[0040] Among them, the silicone macromer represented by the formula(II-1) is preferable, and a silicone macromer represented by the formula(II-1a):

CH₂═C(CH₃)—COOC₃H₆—[Si(CH₃)₂—O]_(d)—CH₃  (II-1a)

[0041] wherein d is a number of 8 to 40,

[0042] is especially preferable. Examples of the silicone macromerinclude a silicone macromer manufactured by CHISSO CORPORATION under thetrade name of FM-0711, and the like.

[0043] The styrenic macromer can be favorably used, from the viewpointof sufficient inclusion of an oil-soluble black dye or carbon black inthe vinyl polymer.

[0044] The styrenic macromer includes styrene homopolymers having apolymerizable functional group at one end, or copolymers of styrene withthe other monomer. Among them, those having acryloyloxy group ormethacryloyloxy group as a polymerizable functional group at one end arepreferable. It is desired that the content of styrene in theabove-mentioned copolymer is at least 60% by weight, preferably at least70% by weight, from the viewpoint of sufficient inclusion of carbonblack in the vinyl polymer. The other monomer mentioned above includesacrylonitrile, and the like.

[0045] It is preferable that the number-average molecular weight of thestyrenic macromer is 1000 to 10000.

[0046] The component (d) includes (meth)acrylates such as methyl(meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (isoor tertiary)butyl (meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl(meth)acrylate, benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,(iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl(meth)acrylate, (iso)stearyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate and 3-hydroxypropyl (meth)acrylate; styrenic monomerssuch as styrene, vinyltoluene, 2-methylstyrene and chlorostyrene; andthe like. These can be used alone or in admixture of at least two kinds.Incidentally, “(iso or tertiary)butyl” means n-butyl, isobutyl ortertiary butyl. Also, “(iso)” means n- or iso.

[0047] It is preferable that the component (d) comprises a styrenicmonomer from the viewpoints of improvements in optical density andhigh-lighter fastness. As the styrenic monomer, styrene and2-methylstyrene are preferable. These styrenic monomers can be usedalone or in admixture thereof. In this case, it is desired that thecontent of the styrenic monomer in the component (d) is 10 to 100% byweight, preferably 40 to 100% by weight, from the viewpoints ofimprovements in optical density and high-lighter fastness.

[0048] It is preferable that the component (d) comprises a hydroxylgroup-containing monomer from the viewpoint of jetting stability in aninkjet printer. As the hydroxyl group-containing monomer, 2-hydroxyethyl(meth)acrylate and 3-hydroxypropyl (meth)acrylate are preferable, andthese can be used alone or in admixture thereof. In this case, it isdesired that the content of the hydroxyl group-containing monomer in thecomponent (d) is 10 to 80% by weight, preferably 15 to 50% by weight,from the viewpoint of jetting stability in an inkjet printer.

[0049] It is desired that the content of the component (a) in the vinylpolymer is 1 to 50% by weight, preferably 5 to 40% by weight, from theviewpoint of dispersion stability of the dispersion obtained.

[0050] It is desired that the content of the component (b) in the vinylpolymer is 5 to 50% by weight, preferably 10 to 40% by weight, from theviewpoints of jetting stability and dispersion stability.

[0051] Also, it is preferable that the total content of the component(a) and the component (b) in the vinyl polymer is 6 to 75% by weightfrom the viewpoints of dispersion stability in water and jettingstability.

[0052] It is desired that the content of the component (c) in the vinylpolymer is 1 to 25% by weight, preferably 5 to 20% by weight, from theviewpoint of increasing the content of the oil-soluble black dye orcarbon black and from the viewpoint of suppressing scorching on theheater surface of an inkjet printer.

[0053] It is desired that the content of the component (d) in the vinylpolymer is 5 to 93% by weight, preferably 10 to 80% by weight, from theviewpoint of suppression of scorching on the heater surface of an inkjetprinter and from the viewpoint of stability. When the component (d)comprising the styrenic monomer is used, it is preferable that thecontent of the component (d) in the vinyl polymer is 10 to 60% byweight. Also, when the component (d) comprising the hydroxylgroup-containing monomer is used, it is preferable that the content ofthe component (d) in the vinyl polymer is 1 to 30% by weight.

[0054] The vinyl polymer is prepared by polymerizing the components (a)to (d) by means of a known polymerization method such as a bulkpolymerization method, a solution polymerization method, a suspensionpolymerization method, an emulsion polymerization method, or the like.Among these polymerization methods, the solution polymerization methodis preferable.

[0055] The solvent used in the solution polymerization method is notlimited to specified ones, and any of water-miscible organic solventsand water-insoluble organic solvents can be used. Examples of thesolvent include an aliphatic alcohol having 1 to 3 carbon atoms; ketonessuch as acetone and methyl ethyl ketone; esters such as ethyl acetate;toluene, and the like. Among them, methanol, ethanol, acetone, methylethyl ketone or mixed solvents thereof with water are preferable.

[0056] Incidentally, a radical polymerization initiator can be used inthe polymerization. As the radical polymerization initiator, any of azocompounds and organic peroxides may be used. It is preferable that theamount of the radical polymerization initiator is 0.001 to 5% by mol,especially 0.01 to 2% by mol based on the total amount of the components(a) to (d).

[0057] In the polymerization, a polymerization chain transfer agent maybe further added. The polymerization chain transfer agent includesmercaptans, xanthogenndisulfides, thiuram disulfides, halogenatedhydrocarbons, and the like. It is preferable that the amount of thepolymerization chain transfer agent is usually 0.001 to 5 parts byweight based on 100 parts by weight of the monomers charged.

[0058] The conditions for polymerizing the components (a) to (d) differdepending upon kinds of the radical polymerization initiator, themonomers and the solvent used, and the like. The polymerizationtemperature is usually 30° to 100° C., preferably 50° to 80° C., and thepolymerization time period is usually 1 to 20 hours. In addition, it ispreferable that the polymerization atmosphere is an atmosphere of aninert gas such as nitrogen gas.

[0059] After the termination of the polymerization reaction, a copolymercan be isolated from the reaction solution by a known method such asreprecipitation or distilling off of the solvent. Also, the resultingcopolymer can be purified by the removal of unreacted monomers and thelike by the repeat of reprecipitation, membrane separation,chromatography or extraction.

[0060] The weight-average molecular weight of the vinyl polymer (asdetermined by the method described in Preparation Example 1) ispreferably 3000 to 200000, more preferably 5000 to 100000, from theviewpoints of jettability, prevention of scorching on a printer head,durability of the water-based ink after printing, and stability of thedispersion.

[0061] The oil-soluble black dyes usable in the present inventioninclude C. I. Solvent Black 3, C. I. Solvent Black 7, C. I. SolventBlack 27, C. I. Solvent Black 29, C. I. Solvent Black 34, Oil Black 860,and the like. Also, the carbon black includes Monarch 880, Monarch 280,Monarch 400, Regal 400R and Mogul L (hereinabove manufactured by CabotCorporation, trade names); PRINTEX-L, PRINTEX-150T, PRINTEX-90,PRINTEX-60 and PRINTEX-80 (hereinabove manufactured by Degussa-AG, tradenames); #950, #960 and MA600 (hereinabove manufactured by MitsubishiChemical Corporation, trade names), and the like.

[0062] It is desired that the total amount of the oil-soluble black dyeand the carbon black is 20 to 400 parts by weight, preferably 30 to 300parts by weight, based on 100 parts by weight of the resin solid contentof the vinyl polymer, from the viewpoints of optical density andfacilitation of inclusion of the black dye or the carbon black into thevinyl polymer.

[0063] The aqueous dispersion of the vinyl polymer particles comprisingthe oil-soluble black dye or the carbon black can be prepared by, forexample,

[0064] (i) a process comprising dissolving the vinyl polymer togetherwith the oil-soluble black dye in a hydrophilic organic solvent, addinga neutralizing agent as occasion demands to cationize or anionize thesalt-forming group of the polymer, adding water to the resultingmixture, and thereafter distilling off the hydrophilic organic solventto phase-invert to a water-based system;

[0065] (ii) a process comprising dissolving the vinyl polymer in anorganic solvent, adding a neutralizing agent as occasion demands tocationize or anionize the salt-forming group of the polymer, addingwater and carbon black thereto and kneading the mixture, and distillingoff the organic solvent from the kneaded product to give a water-basedsystem;

[0066] (iii) a process comprising adding water, a neutralizing agentand, as occasion demands, a surfactant to a solution obtained bydissolving the vinyl polymer and the oil-soluble black dye in awater-insoluble organic solvent, to cationize or anionize thesalt-forming group of the polymer, emulsifying the resulting mixture,and thereafter distilling off the water-insoluble organic solvent togive a aqueous dispersion; or the like.

[0067] The neutralizing agent usable for neutralizing the cationic groupincludes inorganic acids such as hydrochloric acid, nitrous acid,sulfuric acid and phosphoric acid; and organic acids such as acarboxylic acid having 1 to 5 carbon atoms, a dialkyl phosphoric acidhaving 2 to 20 carbon atoms, and oxyacids such as lactic acid, glycolicacid, glyceric acid and gluconic acid. Also, the neutralizing agentusable for neutralizing the anionic group includes alkali metalhydroxides such as sodium hydroxide, potassium hydroxide and lithiumhydroxide; basic substances such as ammonia, triethylamine andmorpholine; alcoholamines such as triethanolamine, diethanolamine andN-methyldiethanolamine, and the like. It is desired that theneutralization degree is adjusted so that the resulting aqueousdispersion becomes neutral.

[0068] The average particle diameter of the vinyl polymer particlesincluding the oil-soluble black dye or the carbon black is preferably0.01 to 0.50 μm, more preferably 0.02 to 0.20 μm, from the viewpoints ofprevention of generation of blotting of the ink and stability of thedispersion.

[0069] The amount of the oil-soluble black dye or the carbon black ispreferably 20 to 400 parts by weight, more preferably 30 to 300 parts byweight, based on 100 parts by weight of the solid content of the vinylpolymer, from the viewpoints of optical density and facilitation ofinclusion of the oil-soluble black dye or the carbon black in the vinylpolymer.

[0070] It is desired that the amount of the water-insoluble vinylpolymer particles containing the oil-soluble black dye or the carbonblack in the water-based ink comprising the aqueous dispersion isadjusted so that the content of the vinyl polymer particles in thewater-based ink is usually 1 to 35% by weight, preferably 2 to 15% byweight, from the viewpoints of optical density and jetting stability.

[0071] The color ink refers to a color ink other than the black ink, forinstance, an ink comprising a pigment or dye which is yellow, magenta,cyan or the like. The color ink includes, an aqueous pigment dispersioncontaining a dispersant, an aqueous dispersion of polymer particlescontaining a pigment or dye, an aqueous solution or aqueous dispersionof a dye, and the like. In addition, the vinyl polymer particles used inthe black ink has an ionicity opposite to that of the color ink.Specifically, for instance, when the ionicity of the vinyl polymerparticles used in the black ink is cationic, the ionicity of the colorink is anionic, and when the ionicity of the vinyl polymer particles ofthe black ink is anionic, the ionicity of the color ink is cationic.

[0072] Here, the ionicity is determined, for example, by potentiometrictitration or determination of pH in the case of a water-soluble dye, orby determination of zeta potential in the case of a dispersion.

[0073] Since the ink is excellent in bleeding resistance (no blotting isgenerated on its periphery) based on that the ionicity of theoil-soluble black dye or the carbon black is opposite to that of thecolor ink, very clear printouts can be obtained.

[0074] The ink set of the present invention may be either a combinationin which an oil-soluble black dye or carbon black used in the black inkis anionic, and the color ink is cationic; or a combination in which anoil-soluble black dye or carbon black used in the black ink is cationic,and the color ink is anionic. Many of anionic dyes show good colordevelopment, and especially acidic dyes are preferable. Therefore, it ispreferable that the black ink is cationic when the color ink is anionic,from the viewpoint of broadening the selection of dyes.

[0075] Further, it is preferable to use an aqueous dispersion of vinylpolymer particles containing a dye or pigment as the color ink from theviewpoints of water resistance and high fixing ability.

[0076] Various additives which have been generally widely used, forinstance, a wetting agent such as a polyhydric alcohol, a dispersant, adefoaming agent, a mildewproof agent, a chelating agent, and the likecan be properly added to the black ink and the color ink in the presentinvention.

[0077] Since the aqueous dispersion of the vinyl polymer particlescontaining the oil-soluble black dye or the carbon black as describedabove is excellent in fixing ability, the aqueous dispersion isexcellent in rubbing resistance, high-lighter fastness, and waterresistance, and shows little blotting.

EXAMPLES

[0078] The units “parts” and “%” as used in each of Examples andComparative Examples are based upon weight.

Preparation Example 1

[0079] A reaction vessel was charged with 20 parts of methyl ethylketone as a polymerization solvent, monomers and a polymerization chaintransfer agent which are listed in the column of initially chargedmonomers of Table 1, and nitrogen gas replacement was sufficientlycarried out.

[0080] On the other hand, after a dropping funnel was subjected tosufficient nitrogen gas replacement, the dropping funnel was chargedwith monomers and a polymerization chain transfer agent which are listedin the column of dropping monomers of Table 1, 60 parts of acetone and0.2 parts of 2,2′-azobis(2,4-dimethylvaleronitrile). The temperature ofthe mixed solution inside the reaction vessel was raised to 65° C. withstirring under nitrogen atmosphere, and the mixed solution inside thedropping funnel was gradually added dropwise thereto over a period of 3hours. After 2 hours passed from the termination of dropping, theretowas added a solution prepared by dissolving 0.1 parts of2,2′-azobis(2,4-dimethylvaleronitrile) in 5 parts of methyl ethylketone. The mixture was further aged at 65° C. for 2 hours and then at70° C. for 2 hours, to give a copolymer solution.

[0081] A part of the resulting copolymer solution was isolated by dryingthe solution at 105° C. for 2 hours under reduced pressure to completelyremove the solvent. The molecular weight was determined by gelpermeation chromatography using polystyrene as a standard substance, andchloroform containing dodecyldimethylamine of 1 mmol/L as a solvent. Asa result, the copolymer had a weight-average molecular weight of 10000.

[0082] The resulting copolymer solution was dried under reducedpressure. To 5 parts of the resulting copolymer were added 25 parts ofan organic solvent listed in Table 1 and 5 parts of an oil-soluble blackdye listed in Table 1, and completely dissolved. To the resultingsolution was added a neutralizing agent (30% aqueous solution) listed inTable 1 with stirring to partly neutralize a salt-forming group of thecopolymer. Thereto was added 300 parts of ion-exchanged water, andthereafter the mixture was emulsified using Microfluidizer (manufacturedby Microfluidizer) for 30 minutes.

[0083] The organic solvent was completely removed from the resultingemulsion at 60° C. under reduced pressure. Further, the mixture wasconcentrated by removing a part of water, to give a cationic aqueousdispersion of vinyl polymer particles containing an oil-soluble blackdye (hereinafter referred to as “BK-1”), the concentration of the solidingredients of which was 10%.

Preparation Example 2

[0084] A copolymer solution was obtained in the same manner as inPreparation Example 1 using the monomers and a polymerization chaintransfer agent which are listed in Table 1. The molecular weight wasdetermined in the same manner as in Preparation Example 1. As a result,the copolymer had a weight-average molecular weight of 10000.

[0085] Five parts of a copolymer obtained by drying the resultingcopolymer solution under reduced pressure was dissolved in 25 parts ofan organic solvent listed in Table 1. To the resulting solution wasadded a neutralizing agent (30% aqueous solution) listed in Table 1 withstirring to partly neutralize a salt-forming group of the copolymer.Thereto were further added 50 parts of ion-exchanged water and 5 partsof carbon black listed in Table 1, and the mixture was kneaded with abeads-mill. The organic solvent was completely removed from theresulting kneaded mixture at 60° C. under reduced pressure. Further, themixture was concentrated by removing a part of water, to give a cationicaqueous dispersion of vinyl polymer particles containing carbon black(hereinafter referred to as “BK-2”), the concentration of the solidingredients of which was 10%.

[0086] Each compound listed in Table 1 means the followings:

[0087] 1) silicone macromer: manufactured by CHISSO CORPORATION underthe trade name of FM-0711;

[0088] 2) styrenic macromer: manufactured by TOAGOSEI CO., LTD. underthe trade name of AS-6 [styrene homopolymerized macromer having anumber-average molecular weight of 6000]; and

[0089] 3) styrene-acrylonitrile macromer: manufactured by TOAGOSEI CO.,LTD. under the trade name of AN-6 [styrene content: 75% by weight,number-average molecular weight: 6000]. TABLE 1 Prep. Ex. No. 1 (BK-1) 2(BK-2) Initially Charged t-Butyl Methacrylate (20) Styrene (9) Monomersand N,N-Dimethylaminoethyl Lauryl Methacrylate (2) PolymerizationMethacrylate (20) N,N-Dimethylaminoethyl Chain TransferMethoxypolyethylene Methacrylate (15) Agent Glycol (n = 9)Methoxypolyethylene (parts) Methacrylate (5) Glycol (n = 4)2-Hydroxyethyl Methacrylate (15) Methacrylate (2) Styrenic MacromerSilicone Macromer AS-6 (5) FM-0711 (2) Mercaptoethanol (0.2)n-Dodecylmercaptan (0.2) Dropping t-Butyl Methacrylate (20) Styrene (10)Monomers and N,N-Dimethylaminoethyl Lauryl Methacrylate (2)Polymerization Methacrylate (20) N,N-Dimethylaminoethyl Chain TransferMethoxypolyethylene Methacrylate (15) Agent (parts) Glycol (n = 9)Methoxypolyethylene Methacrylate (5) Glycol (n = 4) 2-HydroxyethylMethacrylate (20) Methacrylate (2) Styrenic Macromer Silicone MacromerAS-6 (5) FM-0711 (2) Mercaptoethanol (1.8) n-Dodecylmercaptan (1.8)Dye/Pigment Oil Black 860*¹ Carbon Black Monarch 880^(*2) OrganicSolvent Acetone Methyl Ethyl Ketone Neutralizing Glycolic Acid (3.2)Gluconic Acid (5.2) Agent

Preparation Example 3

[0090] Ten parts of carbon black having a surface area of 230 m²/g and aDBP oil absorption of 70 m²/g and 3.06 parts of3-amino-N-ethylpyridinium bromide were thoroughly mixed with 72 parts ofwater. Thereafter, 1.62 parts of nitric acid was added dropwise thereto,and the mixture was stirred at 70° C. After 4 minutes passed, a solutionprepared by dissolving 1.07 parts of sodium nitrite in 5 parts of waterwas added thereto, and the mixture was stirred for additional 1 hour.The resulting slurry was filtered with Toyo Roshi No. 2 (manufactured byADVANTICE), and the carbon black particles were sufficiently washed withwater. This wet cake-like carbon black was re-dispersed in 3000 mL ofwater, and desalted with a reverse osmotic membrane until the electricconductivity attained to 0.2 μs. Further, this liquid dispersion ofcarbon black was concentrated to a carbon black concentration of 10%,thereby giving a cationic, self-dispersible carbon black aqueousdispersion, to the surface of which a group represented by the formula:

[0091] was bonded (hereinafter referred to as BK-3).

Example 1

[0092] A black ink comprising a cationic colorant composed of thefollowing components and anionic color inks of yellow, magenta and cyancomposed of the following components were combined together to give anink set. Each ink was prepared by mixing each of the components, andfiltering with a microfilter having a pore size of 5 μm as to the blackink or with a microfilter having a pore size of 0.45 μm as to the otherinks under pressure, to give an ink. [Components] 1) Black Ink BK-1 80parts Glycerol 5 parts Ethylene Glycol 5 parts Isopropyl Alcohol 2 partsAcetylenol EH (manufactured by Kawaken 2 parts Fine Chemicals Co., Ltd.,trade name) Water 6 parts 2) Color Inks <Yellow> C.I. Acid Yellow 25 4parts Glycerol 5 parts Diethylene Glycol 5 parts Urea 5 parts Sodiumpolyoxyethylene lauryl ether sulfate 1 part [manufactured by KaoCorporation under the trade name of EMAL 20C] Water 80 parts <Magenta>C.I. Acid Red 51 4 parts Glycerol 5 parts ε-Caprolactam 5 parts Urea 5parts EMAL 20C [manufactured by Kao Corporation, 1 part trade name]Water 80 parts <Cyan> C.I. Acid Blue 59 4 parts Glycerol 5 parts2-Pyrrolidone 5 parts Urea 5 parts EMAL 20C [manufactured by KaoCorporation, 1 part trade name] Water 80 parts

Example 2

[0093] The same procedures as in Example 1 were carried out except thatthe black colorant BK-1 was changed to BK-2 in the black ink, to give anink set.

Comparative Example 1

[0094] The same procedures as in Example 1 were carried out except thatan anionic black ink composed of the following components was used asthe black ink, to give an ink set. 1) Black Ink C.I. Direct Black 195 4parts Glycerol 5 parts 2-Pyrrolidone 5 parts Urea 5 parts IsopropylAlcohol 2 parts EMAL 20C [manufactured by Kao Corporation, 1 part tradename] Water 78 parts

Comparative Example 2

[0095] The same procedures as in Example 1 were carried out except thata cationic black ink composed of the following components was used asthe black ink, to give an ink set. 1) Black Ink BK-3 4 parts Glycerol 5parts Urea 10 parts Isopropyl Alcohol 2 parts Acetylenol EH(manufactured by Kawaken 1 part Fine Chemicals Co., Ltd., trade name)Water 78 parts

[0096] The physical properties for the ink sets obtained in Examples 1and 2 and Comparative Examples 1 and 2 were evaluated by the followingmethods. The results are shown in Table 2.

[0097] <Evaluation Methods>

[0098] (1) Printing Property of Black Ink

[0099] An extent of distortion was observed with naked eyes when ruledlines were printed on a regenerated paper for PPC (manufactured byNippon Kako Seishi K.K.) using a commercially available bubble jetprinter manufactured by CANON INC. (model number: BJC-430), andevaluated on the basis of the following evaluation criteria.

[0100] (Evaluation Criteria)

[0101] ⊚: No distortion

[0102] ∘: Little distortion

[0103] Δ: Some distortion

[0104] x: Distortion

[0105] (2) Water Resistance of Black Ink

[0106] Solid image printing was carried out with a black ink on theregenerated paper for PPC by using the above-mentioned printer, anddried at room temperature (about 25° C.) for 1 hour. Thereafter, theprinted copy paper was immersed in stand-still water for 10 seconds, andthe paper was vertically lifted therefrom. After drying the paper in theair at room temperature (about 25° C.), the residual ratio of theoptical density after immersion to the initial optical density wasobtained. The water resistance was evaluated on the basis of thefollowing evaluation criteria:

[0107] (Evaluation Criteria)

[0108] ⊚: Residual ratio being at least 95%

[0109] ∘: Residual ratio being at least 90% and less than 95%

[0110] Δ: Residual ratio being at least 70% and less than 90%

[0111] x: Residual ratio being less than 70%

[0112] (3) Rubbing Resistance of Black Ink

[0113] Solid image printing was carried out with a black ink on theregenerated paper for PPC using the above-mentioned printer. After thepaper was dried for 1 day at room temperature (about 25° C.), theprinted surface was strongly rubbed with a finger. The extent of rub-offof the printed image was observed with naked eyes, and evaluated on thebasis of the following evaluation criteria:

[0114] (Evaluation Criteria)

[0115] ∘: Substantially no printed image being rubbed off, and itsperiphery being not stained.

[0116] Δ: Some printed images being rubbed off, its periphery beingstained, and finger also being stained a little.

[0117] x: Printed images being considerably rubbed off, its peripherybeing considerably stained, and finger also being considerably stained.

[0118] (4) High Lighter-Fastness of Black Ink

[0119] Text printing was carried out with a black ink on the regeneratedpaper for PPC by using the above-mentioned printer. After 6 hourspassed, the extent of staining of the printed sample was observed withnaked eyes after being traced with a commercially available aqueousfluorescent marker, and evaluated on the basis of the followingevaluation criteria:

[0120] (Evaluation Criteria)

[0121] ∘: No stains such as rubbed stains were observed even when tracedwith a fluorescent marker.

[0122] Δ: Some rubbed stains were generated when traced with afluorescent marker, but such stains would cause no problems in practicaluses.

[0123] x: Generation of rubbed stains was observed when traced with afluorescent marker, and the stains were considerably noticeable. (5)Bleeding Resistance Between Black Ink and Color Inks

[0124] Solid image printing was carried out with a black ink out of eachink set on the regenerated paper for PPC by using the above-mentionedprinter. Immediately thereafter, solid image printing of each color inkwas carried out, so that an adjoining portion to the previous solidimage was printed with a yellow, magenta or cyan ink. The boundaryportion of the resulting solid image printing was observed with nakedeyes, and the bleeding between the black ink and the color ink wasevaluated on the basis of the following evaluation criteria.

[0125] (Evaluation Criteria)

[0126] ⊚: No bleeding being recognized on its entire periphery

[0127] ∘: Slight bleeding being recognized but not to be noted

[0128] Δ: Some bleeding being recognized

[0129] x: Noticeable bleeding being recognized on almost the entireperiphery TABLE 2 High Printing Water Rubbing Lighter- Property ofResistance Resistance Fastness Black Ink of of of Bleeding (Distortion)Black Ink Black Ink Black Ink Resistance Ex. No. 1 ⊚ ⊚ ∘ ∘ ∘ 2 ∘ ⊚ ∘ ∘ ∘Comp. Ex. 1 ⊚ x ∘ Δ x 2 Δ Δ x x ∘

[0130] It can be seen from the above results that all of the ink setsobtained in Examples are excellent in printing property, waterresistance, rubbing resistance and high-lighter fastness of the blackink, and also are excellent bleeding resistance.

INDUSTRIAL APPLICABILITY

[0131] Since the ink set of the present invention is excellent injettability, water resistance and fixing ability, and further excellentin bleeding resistance and can form very clear printed characters, theink set can be suitably used as a water-based ink for inkjet recording.

1. An ink set comprising a black ink and a color ink, wherein the blackink comprises an aqueous dispersion of water-insoluble vinyl polymerparticles containing an oil-soluble black dye or carbon black, the vinylpolymer particles have an ionicity opposite to that of the color ink,and the vinyl polymer comprises a water-insoluble vinyl polymer preparedby copolymerizing (a) a salt forming group-containing monomer, (b) amonomer represented by the formula (I): CH₂═C(R¹)COO(R²O)_(p)R³  (I)wherein R¹ is hydrogen atom or a lower alkyl group, R² is a divalenthydrocarbon group which may have a hetero-atom, R³ is a monovalenthydrocarbon group which may have a hetero-atom, and p is a number of 1to 60, (c) a macromer, and (d) a monomer copolymerizable with thesemonomers.
 2. The ink set according to claim 1, wherein the macromer is asilicone macromer represented by the formula (II):X(Y)_(q)Si(R⁴)_(3-r)(Z)_(r)  (II) wherein X is a polymerizableunsaturated group; Y is a divalent group; each of R⁴ is independentlyhydrogen atom, a lower alkyl group, an aryl group or an alkoxy group; Zis a monovalent siloxane polymer residue having a number-averagemolecular weight of at least 500; q is 0 or 1; and r is an integer of 1to 3, and/or a styrenic macromer having a polymerizable functional groupat one end.
 3. The ink set according to claim 1 or 2, wherein theionicity of the vinyl polymer particles is cationic.